Purification of herpes virus

ABSTRACT

The present disclosure provides a method to prepare purified enveloped viral particle preparations employing ion exchange chromatography and tangential flow filtration.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/369,844 (now U.S. Pat. No. 9,365,832), filed 30 Jun. 2014, which is aU.S. National Stage application of PCT/US2013/020780, filed 9 Jan. 2013,which claims the benefit of, and relies on the filing date of, U.S.provisional patent application No. 61/584,461, filed 9 Jan. 2012 andU.S. provisional patent application No. 61/649,625, filed 21 May 2012,the entire disclosures of which are herein incorporated by reference.

FIELD OF THE DISCLOSURE

This disclosure relates to methods for purifying viral particles andcompositions comprising the same.

BACKGROUND OF THE DISCLOSURE

HSV-2 is the primary cause of infectious ulcerative genital diseaseworldwide, with HSV-1 becoming an increasingly important cause ofgenital herpes infection. Worldwide there are an estimated 23 millionnew HSV-2 infections per year. A number of HSV-2 vaccine approaches havebeen tested in the clinic (reviewed by Johnston C, et al., J Clin Invest2011, 121:4600-4609) with varied degree of success. To address the lackof an effective vaccine, a replication defective HSV-2 vaccine strainvirus (dl5-29, which has since been re-derived and renamed ACAM529(Delagrave S, et al. PLoS ONE, 2012 7(10): e46714), also known asHSV529) has been constructed by deleting the U_(L)5 and U_(L)29 genesfrom the wild type virus (Da Costa X, et al., J Virol 2000,74:7963-7971). The vaccine strain virus dl5-29 induces a protectiveimmune response in vivo in mice and guinea pigs without eitherreplication or establishment of latency (Da Costa X J, et al., Proc NatlAcad Sci USA 1999, 96:6994-6998; Hoshino Y, et al., J Virol 2005,79:410-418; Hoshino Y, et al., J Infect Dis 2009, 200:1088-1095).Additionally, dl5-29 was shown to be effective in prevention of latentinfection in guinea pigs irrespective of HSV-1 serostatus (Hoshino Y, etal., J Infect Dis 2009, 200:1088-1095). However, these studies werecarried out with vaccine purified using centrifugation-based methodswhich are not readily scaled for commercial production. Indeed, a numberof groups have defined laboratory-scale procedures for purification ofherpes viruses based upon centrifugation (Arens M, et al., DiagnMicrobiol Infect Dis 1988, 11:137-143; Lotfian P, et al., BiotechnolProg 2003, 19:209-215); gradients (Goins W F, et al., Methods Mol Biol2008, 433:97-113; Sathananthan B, et al., APMIS 1997, 105:238-246; Sia KC, et al., J Virol Methods 2007, 139:166-174; Szilagyi J F, et al., JGen Virol 1991, 72 (Pt 3):661-668); filtration (Knop D R, et al.,Biotechnol Prog 2007, 23:715-721); and affinity chromatography (Jiang C,et al., Biotechnol Bioeng 2006, 95:48-57; Jiang C, et al., J Virol 2004,78:8994-9006).

As with centrifugation-based methods, these other traditionallaboratory-scale purification processes for vaccine strain virusesinvolve laborious procedures that cannot be scaled for commercialproduction of viral compositions prepared in accordance with WorldHealth Organization (WHO) guidelines for human use, resulting in eitherlow yields or insufficient purity (e.g., excessively high levels ofresidual host cell DNA). The World Health Organization (WHO) provides anupper limit of 10 ng host cell DNA per human dose, thus a need exists toprovide virus preparations with less than 10 ng host cell DNA per humandose.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a method to prepare purified envelopedviral particle preparations, including HSV particle preparations,employing ion exchange chromatography and tangential flow filtration.These purification methods can be used to prepare high yield viralpreparations, including HSV preparations (e.g., HSV529), in accordancewith WHO guidelines for human use, including high purity (e.g., lessthan 10 ng host cell DNA per exemplary human dose (e.g., 1×10⁷ PFU)).

Preparation of the vaccine strain virus HSV529 by laboratory-scalevirological methods (including sucrose cushion ultracentrifugation)results in crude material with greater than 2 μg of residual host cellDNA per 1×10⁷ PFU of HSV529 (the World Health Organization limit is 10ng DNA per human dose). The instant disclosure provides a method forpurifying HSV529 in which the amount of residual Vero DNA is below 10 ngper 1×10⁷ PFU of HSV529.

One aspect of this disclosure is directed to a method for thepurification of herpes simplex virus (HSV) particles from a mammalianhost cell culture comprising the steps of:

-   -   a) treating the mammalian host cell culture with a viral        releasing agent, such as dextran sulfate, to release the HSV        particles from the host cells;    -   b) treating the material from step (a) with an endonuclease,        such as Benzonase®;    -   c) filtering the material from step (b) to remove any intact        cells or cellular debris;    -   d) applying the solution obtained from step (c) to an anion        exchange chromatography resin;    -   e) eluting the HSV particles from the anion exchange column;    -   f) subjecting the eluent from step (e) to tangential flow        filtration; and    -   g) recovering the purified HSV particles.

In some embodiments, the purified HSV particles contain greater than1×10⁷ or 2×10⁷ PFU/mL. In other embodiments, the purified HSV particlescontain less than 10 ng host cell DNA per 1×10⁷ plaque forming units(PFU). In one embodiment, the HSV is a replication defective HSV, suchas HSV529.

In yet another embodiment, the tangential flow filtration is a hollowfiber system. In one embodiment, the hollow fiber system has a molecularweight cutoff of 100 kDa. In another embodiment, the anion exchangechromatography comprises a membrane-based chromatography resin, such asthe Mustang® Q (Pall Life Sciences) resin.

Another aspect of the disclosure is directed to a pharmaceuticalcomposition comprising Herpes Simplex Virus (HSV) produced in amammalian cell culture, said HSV isolated by the method comprising thesteps of:

-   -   a) treating the host cell culture with a viral releasing agent,        such as dextran sulfate, to release HSV particles from the host        cells;    -   b) treating the product of step (a) with an endonuclease, such        as Benzonase®, to reduce residual host cell DNA;    -   c) filtering the product of step (b) to remove any intact cells        or cellular debris;    -   d) applying the filtrate of step (c) to an anion exchange        chromatography resin;    -   e) eluting the HSV particles from the anion exchange column;    -   f) subjecting the eluent from step (e) to tangential flow        filtration;    -   g) recovering the purified HSV particles; and    -   h) suspending the purified HSV particles in a pharmaceutically        acceptable carrier.

In one embodiment, the quantity of host cell DNA in said composition isless than 10 ng host cell DNA per 1×10⁷ plaque forming units (PFU). Inanother embodiment, the HSV is a replication defective HSV, such asHSV529. In other embodiments, the composition contains greater than1×10⁷ PFU/mL, preferably between about 1×10⁷ to 2×10⁷ PFU/mL.

Another aspect of the disclosure is directed to a composition comprisingHerpes Simplex Virus (HSV) particles in a liquid stabilization buffer,wherein the liquid stabilization buffer comprises potassium glutamate,histidine, a salt, and a sugar. In one embodiment, the liquidstabilization buffer comprises 20-75 mM potassium glutamate, 1-20 mMhistidine, 50-250 mM salt, and 5-20% sugar. In another embodiment, theliquid stabilization buffer comprises 50 mM potassium glutamate, 10 mMhistidine, 160 mM salt, and 10% sugar. In one embodiment, the sugar issucrose. In another embodiment, the pH of the liquid stabilizationbuffer is about 7.5. In one embodiment, the HSV is a replicationdefective HSV, such as HSV529. In another embodiment, the quantity ofhost cell DNA in said composition is less than 10 ng host cell DNA per1×10⁷ plaque forming units (PFU). In other embodiments, the compositioncontains greater than 1×10⁷ PFU/mL, preferably between about 1×10⁷ to2×10⁷ PFU/mL.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 provides a schematic representation of one embodiment of thepresent disclosure for the preparation of material comprising areplication deficient recombinant herpes virus known as HSV529 producedin complementing producer cell lines.

FIGS. 2A-B show the results of the chemical elution of HSV529 from thesurface of infected AV529-19 complementing cells at 2 days postinfection (“2 dpi”) (FIG. 2A) and at 3 days post infection (“3 dpi”)(FIG. 2B). The cell culture medium was decanted from confluent, infectedAV529-19 cells grown in 12-well tissue culture plates and replaced withstability buffer containing 10% sucrose and 25-500 μg/mL dextran sulfate(DS). At 3 h (0), 5 h (▪), 8 h (▴) and 24 h (▾) after the start of thedextran sulfate elution the samples were processed by centrifugation at1,000×g and freezing at −80° C. prior to titration by plaque assay. Theresults represent the titer (PFU/mL) of the DS release supernatant, theerror bars represent the standard deviation of the mean.

FIG. 3 shows the chromatographic profile during small scale (0.35 mLMustang® Q coin) bind-and-elute purification of HSV529 by membrane-basedanion exchange. The solid line represents the elution profile forabsorbance at 280 nm, whereas the dotted line represents theconcentration of salt as a percentage of the high salt buffer (Buffer B,2 M NaCl). During the sample loading phase (0-50 mL) HSV529 bound thesolid support, while unbound impurities passed through the column andwere collected as the flowthrough fraction. Pre-elution of bound,non-viral protein impurities was achieved by applying a 700 mM NaCl (30%B) step over 30 column volumes (50-60 mL). Bound HSV529 was eluted fromthe column by step-wise increase of the salt concentration to 2 M NaCl(100% Buffer B) over 30 CV (60-70 mL).

FIG. 4 shows the results of optimization of purification conditions toachieve a yield of 400 human doses per NUNC cell factory. Each of thepoints on the curve represents the yield from an entire purification,starting with material which had been dextran sulfate-released from asingle NCF of infected cell culture. HSV529 Purifications A-G wereperformed sequentially, with optimization of purification steps toimprove yield and purity. The overall yield (y-axis; doses per NCF)increased with time as purification conditions were optimized. Flatsheet TFF was originally tested as an option for concentration andformulation of the partially purified vaccine virus (HSV529 PreparationsA-D). Low step yield for flat sheet TFF (˜20-40%) led to testing ofhollow fiber TFF as an alternative (Preparations E-G), with dramaticimprovement (˜70-100% step yield) of recovery of infectious virus.Additionally, the high-capacity strong anion exchanger, Fractogel TMAEHiCap (BEAD, Preparation G) was tested as an alternative to Mustang® Q(MEMBRANE, Preparations A-F) as the bind-and-elute chromatography step.

FIGS. 5A-D show the purity of HSV529 virus preparations. The tablesprovide superimposition of yield (●) (FIG. 5A) with purity (

) (FIGS. 5B-D) results for HSV529 Preparations A-G. The right y-axes inFIGS. 5B-D represent results from purity assays: residual Vero DNA qPCR,LOQ≤1 pg/μL (FIG. 5B), DS ELISA, LOD 3 ng/mL (FIG. 5C) and Vero HCPELISA, LOD 2 ng/mL (FIG. 5D). In FIG. 5C, for preparations A-F, and FIG.5D, preparation D, where no purity data point is present, the amount ofimpurity in the final material was below the assay-specific LOD. In allcases, the purity of Preparation F exceeded that of Preparation G,exemplifying why the Preparation F conditions were decided upon for useas the final purification scheme.

FIGS. 6A-C demonstrate that chromatography-purified HSV529 is asimmunogenic and protective as sucrose cushionultracentrifugation-purified HSV529. FIG. 6A is a schematicrepresentation of the animal study schedule, long labeled arrowsrepresent viral inoculations (immunizations were performed sc andchallenge was intravaginal) short arrows symbolize bleeds, hormoneinjection (DMPA=depot medroxyprogesterone acetate or Depo-Provera) andthe study end day, as indicated. FIG. 6B shows endpoint ELISA titersagainst a commercially available, purified HSV-2 viral lysate forimmunized mice and FIG. 6C depicts survival of animals as a % of thetotal (n=15 animals). Mice were immunized either with Mustang® Q (●) orsucrose cushion (▴)-purified HSV529 or a placebo (♦)(PBS). Both vaccinepreparations elicited similar anti-HSV-2 ELISA titers (Kruskal-WallisTest P=0.99) and similar levels of protection against severe viruschallenge with wild type HSV-2 strain 333 (Mantel-Cox Test P<0.0001).

DETAILED DESCRIPTION OF THE DISCLOSURE

In order to advance development of Herpes Simplex Virus (HSV) vaccines(e.g., HSV529) beyond animal models and into clinical studies, ascalable process capable of producing viral material suitable for humanuse was developed. A highly-purified, functional version of HSV529 wasmade by processing of infected complementing Vero cells (AV529-19) by acombination of dextran sulfate elution followed by endonucleasetreatment, depth filtration, anion exchange chromatography and UF/DF(via tangential flow filtration). The overall yield for the optimizedprocess is 10-20% of the infectious titer in the starting material,which equates to 100-300 doses per NUNC Cell Factory (NCF) (variabilityin the vaccine titer in the starting material accounts for thediscrepancy between yield and number of doses purified per NCF).Importantly, this purification scheme yields virus that is sufficientlypure with respect to residual Vero genomic DNA for testing in humans(i.e., less than 10 ng residual host cell DNA per 1×10⁷ PFU).

In one aspect, the present disclosure provides a method for thepurification of an enveloped viral particle, such as a Herpes SimplexVirus (HSV) particle, from a mammalian host cell culture comprising thesteps of:

-   -   a) treating the mammalian host cell culture with a viral        releasing agent (e.g., dextran sulfate) to release the enveloped        viral particles from the host cells without significant lysis of        the host cells;    -   b) applying the solution obtained from step (a) to an anion        exchange chromatography resin;    -   c) eluting the enveloped viral particles from the anion exchange        column;    -   d) subjecting the eluent from step (c) to tangential flow        filtration, and    -   e) recovering the purified enveloped viral particles.

The present disclosure further provides a method for the purification ofan enveloped viral particle, such as an HSV particle, from a mammalianhost cell culture comprising the steps of:

-   -   a) treating the mammalian host cell culture with a viral        releasing agent (e.g., dextran sulfate) to release the enveloped        viral particles from the host cells without significant lysis of        the host cells;    -   b) subjecting the solution obtained from step (a) to tangential        flow filtration;    -   c) applying the retentate from the tangential flow filtration        step to an anion exchange chromatography resin;    -   d) eluting the enveloped viral particles from the anion exchange        column; and    -   e) recovering the purified enveloped viral particles.

The disclosure further provides a method as provided in the foregoingwherein before applying the solution obtained from step (a) to the anionexchange chromatography resin the solution obtained from step (a) istreated with an endonuclease (e.g., Benzonase®) to degrade residual hostcell DNA.

The disclosure further provides a method as provided in the foregoingfurther comprising the step of clarifying the product material by depthfiltration prior to anion exchange chromatography to remove any intactcells and/or cellular debris.

The disclosure further provides a method for the purification and thepreparation of purified preparations of recombinant herpesvirusparticles, in particular replication defective herpes simplex viralparticles, such as HSV529 particles.

The viral (e.g., HSV) particles purified according to these methods areproduced in high yield with sufficient purity that they can beadministered to a human and preferably contain less than 10 ng residualhost cell DNA per 1×10⁷ PFU. In some embodiments, the purified viral(e.g., HSV) particles contain greater than 1×10⁷ or 2×10⁷ PFU/mL. Inanother embodiment, the purified viral (e.g., HSV, including but notlimited to HSV529) particles contain about 10-20% of the infectioustiter of virus in the solution obtained by treating the mammalian hostcell culture with a viral releasing agent, such as Benzonase®.

The endonuclease is preferably one that degrades both DNA and RNA. Inone embodiment, the endonuclease is a genetically engineeredendonuclease from Serratia marcescens (Eaves, G. N. et al. J. Bact.1963, 85, 273-278; Nestle, M. et al. J. Biol. Chem. 1969, 244,5219-5225) that is sold under the name Benzonase® (EMD Millipore). Theenzyme is produced and purified from E. coli strain W3110, a mutant ofstrain K12, containing the pNUC1 production plasmid (U.S. Pat. No.5,173,418, which is hereby incorporated by reference in its entirety).Structurally, the protein is a dimer of identical 245 amino acid, ˜30kDa subunits with two important disulfide bonds. Benzonase® degrades allforms of DNA and RNA (single stranded, double stranded, linear andcircular) and is effective over a wide range of operating conditions,digesting nucleic acids to 5′-monophosphate terminated oligonucleotides2-5 bases in length. Benzonase® is produced under current goodmanufacturing practices (cGMP) and, thus, can be used in industrialscale processes for the purification of proteins and/or viral particles.Other endonucleases that are produced under cGMP conditions can likewisebe used in the purification methods disclosed in this application.

In some embodiments, the purified preparations comprise viral particles,including HSV particles, in a liquid stabilization buffer. The liquidstabilization buffer may comprise, for example, potassium glutamate, atleast one amino acid (e.g., histidine), at least one salt (e.g., sodiumchloride), and/or at least one sugar (e.g., sucrose, trehalose, and/orsorbitol). An exemplary liquid stability buffer may comprise, forexample, about 20-75 mM potassium glutamate (e.g., 50 mM potassiumglutamate), about 1-20 mM histidine (e.g., 10 mM histidine), about50-250 mM salt (e.g., 0.16 M sodium chloride), and about 5-20% sugar(e.g., 10% sucrose, trehalose, and/or sorbitol) at an appropriate pH(e.g., about any of pH 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7. or 7.8,especially about pH 7.5). Thus, for example, a suitable liquid stabilitybuffer may comprise or consist of 50 mM potassium glutamate, 10 mMhistidine, 160 mM sodium chloride, 10% sucrose, pH 7.5. In oneembodiment, the HSV particle in the liquid stabilization buffer is areplication defective HSV, such as HSV529.

The disclosure further provides a pharmaceutically acceptable dosageform of an enveloped viral vector, such as a HSV vector, produced in amammalian cell culture, said enveloped viral vector being isolated by amethod comprising the steps of:

a) treating the host cell culture with a viral releasing agent (e.g.,dextran sulfate) to release the enveloped viral particles from the hostcells without significant lysis of the host cells,

b) treating the product of step (a) with an endonuclease (e.g.,Benzonase®) to reduce residual host cell DNA;

c) filtering the product of step (b) to remove any intact cells orcellular debris;

d) applying the filtrate of step (c) to an anion exchange chromatographyresin;

e) eluting the enveloped viral particles from the anion exchange column;

f) subjecting the eluent from step (e) to tangential flow filtration;

g) recovering the purified enveloped viral particles;

h) concentrating the viral particles by diafiltration; and

i) suspending the purified enveloped viral particles in apharmaceutically acceptable carrier to a final concentration of greaterthan 1×10⁷ PFU/mL.

In another embodiment, the final concentration is at least 2×10⁷ PFU/mL.The disclosure further provides a pharmaceutically acceptable dosageform of an enveloped viral vector produced in a mammalian cell culturewherein the residual host cell DNA in said composition is less than 10ng host cell DNA per 1×10⁷ PFU. In one embodiment, the enveloped virusis a replication defective HSV, such as HSV529, as discussed in furtherdetail below.

The viral particles obtained by the purification methods describedherein retain infectivity following purification such that they can beused to induce a protective immune response when administered to amammal. Thus, HSV529 particles purified according to the methodsdescribed herein induce a protective immune response when administeredsubcutaneously to BALB/c mice, as demonstrated in Example 10.

Typical mammalian cell hosts for enveloped viruses are well known tothose of skill in the art and are readily available from public andprivate depositories. Particularly useful for the production of virusesexemplified here for purposes of the present disclosure include theVero, HEK293, MDK, A549, EB66, CHO and PERC.6.

Herpes viruses include members of the genus herpesviridae including butnot limited to HSV-1, HSV-2, varicella zoster virus, Epstein-Barr virus,and cytomegalovirus. Herpes Simplex Type-1 (HSV-1) and Type-2 (HSV-2)viruses are members of the alphaherpesvirus subfamily that causeprevalent, lifelong genital, dermal and ocular infections resulting in aspectrum of clinical manifestations that includes cold sores, genitalulceration, corneal blindness and encephalitis. Genital herpes simplexvirus infection is a recurrent, lifelong disease with no cure, and novaccines are available. While HSV-2 is the most common cause of genitalulcers, HSV-1 is becoming an increasingly important cause of genitalherpes infection. HSV is an enveloped, linear, double-stranded DNA viruswhose only known hosts are humans. HSV-1 and HSV-2 share 83% sequencehomology of their protein-coding regions and the structure of theirgenomes are alike. They are distinguished by antigenic differences inthe respective envelope proteins.

One example of a herpes virus useful in the practice of the presentdisclosure is HSV529 (previously known as dl5-29 and ACAM529), areplication-defective herpes virus (parent strain 186 syn+−1)genetically modified to contain 2 gene deletions: U_(L)5 and U_(L)29 asmore fully described in Da Costa, et al (2000) J. Virology 74:7963-7971and WO 99/06069, the disclosures of which are hereby incorporated byreference in their entirety. The original dl5-29 strain was re-derivedand renamed as ACAM529 (Delagrave S, et al. PLoS ONE, 2012 7(10):e46714), which is also known as HSV529. Thus, the terms dl5-29, ACAM529and HSV529 are used interchangeably throughout this application. The UL5deletion consists of removal of the UL5 gene and part of thenonessential UL4 open reading frame (ORF) from nucleotides 12,244 to15,143. The UL5 gene is an essential component of the viralhelicase-primase complex and is required for viral DNA synthesis. TheUL29 deletion consists of removal of the complete UL29 gene fromnucleotides 58,784 to 62,527. The UL29 gene encodes the viralsingle-stranded DNA binding protein ICP8 (infected cell protein 8),which is essential for viral DNA synthesis. Together, this doublemutation results in a virus that only grows on a complementary cellline, AV529-19 Vero cells containing the UL29 and UL5 genes and does notgrow on normal Vero cells.

The strategy of introducing two mutations reduces the potential forgeneration of replication-competent virus due to recombination withendogenous gene in the propagating cell line or recombination withwild-type HSV in the host. Propagation of HSV529 on a large scale isachieved by growth of the virus under serum free conditions on itsrecombinant complementing cell line AV529-19 (derived from Vero CCL-81.2(African green monkey) cells). HSV529 displays a similar pattern ofprotein expression on AV529-19 Vero cells compared to wild type virus onVero cells with the exception that ICP8 is not expressed, and lateproteins ICP5, gB, and ICP25, are expressed at lower levels compared towild-type virus.

There is a range of time after infection of the host cells where themaximum amount of virus can be released from the cells. The timing ofrelease varies depending on the temperature, the infection media used,the virus which was used to infect the cells, the container in which thecells were grown and infected and the cells themselves. Identificationof this optimal harvest time is readily determined by sampling of thecell culture regularly over the conventional incubation period for theparticular enveloped virus to determine the optimal yield. Under theconditions tested (Vero cells and HSV529), the maximum virus wasreleased from the host cells between approximately 24 and 72 hours afterinfection.

Rather than harvesting the entire cell culture and lysing the host cellsand attempting to isolate the newly produced viral particles from thecomplex cell milieu, it is preferred that the newly formed viralparticles be isolated from the surface of the intact host cells. Thiscan be accomplished by exposure of the host cells to a viral releasingagent. Such viral releasing agent is any agent that is capable ofdisruption of the interaction between the viral particle and the cellsurface. In one embodiment, the viral releasing agent is dextransulfate. In the practice of the present disclosure, the viral particlesare preferably dislodged from the cell surface with solutions containingdextran sulfate, serum free media or phosphate buffered saline. In oneembodiment, the viral releasing agent is a solution of the followingcomponents: 50 mM potassium glutamate, 10 mM histidine, 0.16 M sodiumchloride, 100 μg/mL dextran sulfate MW 6-8 kDa, 10% sucrose, pH 7.5)(e.g., a liquid stability buffer further including dextran sulfate). Itwas determined experimentally that exposure of the cell culture to thisviral releasing agent for 24 hours produced the highest yields. Based onexperimentation, it is desirable that the culture be exposed to thereleasing agent for at least 3 hours, at least 5 hours, at least 8hours, or between 20 and 24 hours.

When performing a depth filtration procedure prior to anion-exchangechromatography, endonuclease treatment of the viral preparation prior todepth filtration improves the efficiency of the process by minimizingfouling of the depth filtration matrix. Alternatively, even in theabsence of a depth filtration step, the recovery of virus from thechromatographic step was diminished when non-endonuclease treated viruswas applied to this and other chromatographic supports.

As understood in the art, depth filtration refers to the use of a porousfilter medium to clarify solutions containing significant quantities oflarge particles (e.g., intact cells or cellular debris) in comparison tomembrane filtration which would rapidly become clogged under suchconditions. A variety of depth filtration media of varying pore sizesare commercially available from a variety of manufacturers such asMillipore, Pall, General Electric, and Sartorious. In the practice ofthe disclosure as exemplified herein, SartoScale disposable SartopurePP2, 0.65 μm depth filters (Sartorious Stedim, Goettingen, Germany) wereused. Use of this system resulted in no appreciable loss of virus titer.

The principles of anion exchange chromatography are well known in theart, but, briefly, this method relies on the charge-charge interactionsbetween the particles to be isolated and the charge on the resin used.Since most viruses are negatively charged at physiological pH ranges,the column contains immobilized positively charged moieties. Generallythese are quaternary amino groups (Q resins) or diethylaminoethanegroups (DEAE resin). In the purification of large particles such asviruses, it has been demonstrated that monolithic supports with large(e.g. >1 micron) pore sizes permit purification of macromolecules suchas viruses. Examples of commercially available anion exchange resinsuseful in the practice of the present disclosure include, but are notlimited to, the Mustang® Q (Pall Life Sciences) and the Fractogel TMAE(Merck) resins.

Traditionally, anion exchange resins have been offered and used in thebead format, for example Q Sepharose™ available from GE HealthcareBio-Sciences AB. Thus, in one embodiment, the anion exchangechromatography comprises a bead-based chromatography resin. However,throughput limitations of bead-based systems require large volumecolumns to effectively capture impurities. In bead-based chromatography,most of the available surface area for adsorption is internal to thebead. Consequently, the separation process is inherently slow since therate of mass transport is typically controlled by pore diffusion.

In another embodiment, the anion exchange chromatography comprises amembrane-based chromatography resin, such as the Mustang® Q resin.Membrane-based chromatographic systems have the ligands attacheddirectly to the convective membrane pores, thereby reducing the effectsof internal pore diffusion on mass transport.

Tangential Flow Filtration (TFF) (also referred to as Cross FlowFiltration CFF) is well known to those of skill in the art and equipmentand protocols for its implementation in a wide range of situations arecommercially available from a variety of manufacturers including but notlimited to the Pall Corporation, Port Washington, N.Y. and SpectrumLabs, Rancho Dominguez, Calif. Generally, TFF involves the recirculationof the retentate across the surface of the membrane. This gentle crossflow feed minimizes membrane fouling, maintains a high filtration rateand provides high product recovery. In one embodiment, the TFF step maybe implemented with a flat sheet system, as exemplified herein. Flatsheet systems are generally preferred in large scale production wheresuch systems are provided with a means (e.g., an open flow channel) toprevent excessive shear forces on the enveloped viral particles.Alternatively, the TFF step may be implemented with a hollow fibersystem, as exemplified herein. In one embodiment, the Molecular WeightCut Off (MWCO) of the TFF system is between 250-50 kDa, preferably about200 kDa or 100 kDa.

One embodiment of the present disclosure is directed to a method ofpreparing high-titer HSV529. After propagation of HSV529 in thecomplementing cell line, it is necessary to purify the virus from thecellular material and cell culture media components before further use.FIG. 1 represents a detailed flow diagram of an exemplary embodiment ofthe method. Briefly, at 72 hours post infection (hpi), the infectionmedia is decanted from one or more NUNC cell factories (NCF's). Asterile, disposable funnel is placed into the NCF inlet port, and 600 mLof pre-warmed (34° C.) dextran sulfate elution buffer is poured into theNCF. The NCF is then flipped into the cap-up position and placed into ahumidified, 5% CO₂ incubator at 34° C. for 24 h. After 24 h ofincubation, the elution buffer is decanted from the NCF and clarified bycentrifugation for 20 min. at 1,000×g in a centrifuge equipped with aswinging bucket rotor. The HSV529-containing supernatant is decanted andprepared for subsequent Benzonase® endonuclease digestion. If previouslyfrozen, DS-released material is quick-thawed by placing at 37° C. Thesolution is adjusted to five mM MgCl₂ and ninety units of Benzonase® areadded per mL of HSV529-containing solution. The solution should beincubated in a shake flask at 25° C., 80 rpm for 4-6 h. Prior toperforming chromatography, the Benzonase®-treated solution is furtherclarified by depth filtration to remove any remaining cellular debris oraggregated material that could clog the chromatographic membrane.Chromatographic separation is performed by bind-and-elute anion exchangechromatography preferably utilizing the Mustang® Q membrane manufacturedby Pall Life Sciences. Sodium chloride is utilized to elute bound HSV529from the chromatographic support. Finally, concentration and formulationof HSV529 is performed, preferably by hollow-fiber tangential flowfiltration (TFF) using a 100 kDa polysulfone (PS) hollow fiber module.

In the case of herpes virus particles, the size of the virus particle(200-250 nm) makes sterile filtration of the material difficult becausethe use of a standard sterilization filter (0.22 μm) results in asignificant loss of material. For example, after filtering the HSV529herpes virus through a 0.8 μm filter, 57.5% of infectious virus wasrecovered, in contrast to only 25.5% of the infectious virus that wasrecovered after filtering through a 0.45 μm filter. Thus, in the case oflarger particles, like herpes virus particles, the process may beperformed under sterile conditions.

Hydrodynamic shear stress played a role in the loss of infectious virustiter. In nearly all cases, when high-shear systems (closed channel flatsheet TFF and bead-based chromatographic support) are replaced bylow-shear unit operations (open channel hollow fiber TFF andmembrane-based chromatographic support) more infectious virus isrecovered per step of the purification process. Without intending to bebound by any theory, it appears that convective liquid flow, as in thecase of membrane (Mustang® Q) and monolithic (CIM) chromatographicsupports, minimizes shear by eliminating flow vortices and turbulenteddies, which occur in the void space in traditional packed beadcolumns. Shear does not entirely explain recovery as is clear from thedifference in yield of infectious virus from the membrane vs. themonoliths tested here.

Apart from optimization of chromatography, the most significant processchange was from flat-sheet, closed-channel TFF to hollow fiber TFF. Thisresulted in up to a 10-fold increase in yield without compromisingpurity. Plaque assay results show that optimization of purificationsteps results in additional increases in yield without compromisedpurity in the case of the Mustang® Q anion exchanger. In contrast,Fractogel TMAE HiCap (a bead-based, strong anion exchanger)-purifiedmaterial appears less attractive in that the final material containsabout 2-fold more residual DNA and at least 2 orders of magnitude moredextran sulfate. Nevertheless, Fractogel TMAE HiCap might still beconsidered as a candidate chromatography resin because chromatographyelution conditions could be optimized to improve purity.

Thus, the data reported in this application support the use ofchromatography-based purification processes for preparation of HSV529,as well as other live-attenuated or replication-defective viralvaccines, suitable for testing in humans.

The herpes virus particles purified according to the present disclosure(e.g., enveloped viral particles contained within a liquid stabilitybuffer) can be formulated according to known methods to preparepharmaceutically useful compositions. The compositions of the disclosurecan be formulated for administration to a mammalian subject, preferablya human, using techniques known in the art. In particular deliverysystems may be formulated for intramuscular, intradermal, mucosal,subcutaneous, intravenous, injectable depot type devices or topicaladministration. When the delivery system is formulated as a solution orsuspension, the delivery system is in an acceptable carrier, preferablyan aqueous carrier. A variety of aqueous carriers may be used, e.g.,water, buffered water, 0.8% saline, 0.3% glycine, hyaluronic acid andthe like. These compositions may be sterilized by conventional, wellknown sterilization techniques, or may be sterile filtered. Theresulting aqueous solutions may be packaged for use as is, orlyophilized, the lyophilized preparation being combined with a sterilesolution prior to administration.

The compositions may contain pharmaceutically acceptable auxiliarysubstances as required to approximate physiological conditions, such aspH adjusting and buffering agents, tonicity adjusting agents, wettingagents and the like, for example, sodium acetate, sodium lactate, sodiumchloride, potassium chloride, calcium chloride, sorbitan monolaurate,triethanolamine oleate, etc.

In particular, such pharmaceutical preparations may be administered tomammalian subjects to induce an immune response in the mammaliansubject. The intensity of such immune response may be modulated bydosage to range from a minimal response for diagnostic applications(e.g. skin testing for allergies) to a durable protective immuneresponse (immunization) against challenge.

In order to enhance the immune response to the viral particle, suchpharmaceutical preparations may optionally include adjuvants. Examplesof adjuvants include aluminum salts (e.g. potassium aluminum sulfate,alum, aluminum phosphate, aluminum hydroxyphosphate, aluminumhydroxide), 3D-MPL, oil-in-water emulsions including but not limited toAS03, AF03, AF04, MF-59, and QS21.

EXAMPLES

The following examples are to be considered illustrative and notlimiting on the scope of the disclosure described above. The followingTable 1 provides a summary of the reagents and materials used in thefollowing examples.

TABLE 1 Reagent/Material Sources Component/Kit Supplier Catalog No. LotNo. Potassium Glutamate Sigma G1501 125K0170 Histidine Sigma H6034056K0002 Sodium Chloride Sigma H7653 098K0098 Multi-Compendial J. T.Baker 4005-06 E44627 Sucrose 1M Magnesium G R004 072702 ChlorideBiosciences Dextran Sulfate Polydex N/A DS8-018R Benzonase ® EMD/Merck1.01697.0002 K38806697 Endonuclease Benzonase ® EMD/Merck 1.01681.0002K92932881 ELISA Kit Vero HCP ELISA Cygnus Tech. F500 8098 Kit DextranSulfate Lifespan Tech. K-3800 6011 ELISA Kit 1 L 0.22 μm filter Nalgene73520-986 (VWR) na apparatus 2 L PETG Bottle Nalge/NUNC 16159-138 (VWR)na 1 L PETG Bottle Nalge/NUNC 16159-136 (VWR) na 500 mL PETG BottleNalge/NUNC 16159-134 (VWR) na 250 mL PETG Bottle Nalge/NUNC 16159-132(VWR) na 125 mL PETG Bottle Nalge/NUNC 16159-130 (VWR) na 1.5 mLEppendorf VWR  20170-038 na Tubes 250 mL Centrifuge Corning 430776 naTube Silicone MasterFlex Cole-Parmer 96410-24 na Tubing(24) SiliconeMasterFlex Cole-Parmer 96410-25 na Tubing (25) 0.35 mL Mustang ® PallLife MSTG18Q16 na Q coin Sciences 10 mL Mustang ® Pall Life CLM05MSTGQP1IL6954 Q capsule Sciences SartoScale, Sartorius 5595305PS-FF 080620SartoPure PP2 Stedim MidiKros Module Spectrum X2AB-200-02P 3241559 (100kDa, PS) LabsStock Buffer Solutions:

-   -   Dextran Sulfate Elution Buffer (50 mM potassium glutamate, 10 mM        histidine, 0.16 M sodium chloride, 100 μg/mL dextran sulfate MW        6-8 kDa, 10% sucrose, pH 7.5)    -   Stability Buffer/Column Equilibration Buffer (50 mM potassium        glutamate, 10 mM histidine, 0.16 M sodium chloride, 10% sucrose,        pH 7.0)    -   Step 1 Chromatography Elution Buffer (50 mM potassium glutamate,        10 mM histidine, 0.7 M sodium chloride, 10% sucrose, pH 7.0)    -   Step 2 Chromatography Elution Buffer (50 mM potassium glutamate,        10 mM histidine, 2 M sodium chloride, 10% sucrose, pH 7.0)    -   1 M sodium chloride    -   1 M magnesium chloride

The following process is illustrative of the practice of the presentdisclosure in relation to the purification of the recombinant herpesvirus HSV529. The process was carried out in five steps:

-   -   1. Dextran sulfate release of HSV529 from infected cells,    -   2. Benzonase® endonuclease digestion of residual DNA,    -   3. clarification by depth filtration (i.e., filtering to remove        any intact cells or cellular debris),    -   4. bind-and-elute purification by anion exchange chromatography        and    -   5. buffer exchange/concentration by tangential flow        ultrafiltration/diafiltration (UF/DF).        Each of these steps is described in more detail below.

Example 1. Cells, Master Virus Seed, and Upstream Process

HSV529 production was accomplished by infection of a monolayer ofcomplementing Vero cells (cell line AV529-19). Complementing cells wereobtained as follows: African Green Monkey (Vero) ATCC cell line CCL-81.2was stably transfected with plasmids pCId.UL5, pcDNA.UL29 and pSV2neo,which were provided by Dr. David Knipe (Harvard Medical School).Populations of cells were screened and clone AV529-19 was selected forits ability to best complement dl5-29 (as ACAM529 was previously knownin the literature). The cell line has been grown and maintained inOptiPro (Life Technologies, Carlsbad, Calif.) supplemented with 4 mMglutamine (Hyclone, Logan, Utah) and 10% FBS (Life Technologies) at 37°C. in a 5% CO₂ atmosphere. Cell culture conditions for the purpose ofinfection and production of ACAM529 will be described below. Thepre-master virus seed (preMVS) used to produce the ACAM529 master virusseed (MVS) was prepared in several steps from an original stock ofdl5-29 as follows: the dl5-29 virus was propagated using complementingVero cells, viral genomic DNA was extracted from the resulting virus andprovided by Dr. David Knipe (Harvard Medical School) for transfectioninto AV529-19 cells, and the resulting virus amplified by a singlepassage. Viral genomic DNA was extracted from this amplified passage andtransfected into AV529-19 cells under GLP conditions. The resultantvirus was harvested, amplified by one passage, plaque-purified fourtimes, amplified by passaging, and banked as the pre-MVS. The ACAM529master virus seed (MVS) was prepared and banked under GMP using thepre-MVS and AV529-19.

Development was undertaken in order to determine upstream growth andinfection conditions. Experiments were first performed at the smallscale (12-well tissue culture plate and T125 flask) and eventuallyscaled up to production in NUNC cell factories (NCF's) with a workingvolume of 2 L and 6,320 cm² cell culture area. For clarity, upstreamgrowth conditions are presented at the NCF scale. A single NCF wasseeded with 3.8×10⁸ serum-free AV529-19 cells in OptiPro mediasupplemented with 4 mM GlutaMAX (Life Technologies) and 500 μg/mL G418(Life Technologies). The cells were grown at 37° C. in a 5% CO₂humidified incubator, with a single medium change at 48 h to 1.3 L 40%OptiPro diluted in Dulbecco's phosphate buffered saline (DPBS) andsupplemented with 0.5× cholesterol lipid concentrate (Life Technologies)and 50 mM sucrose. Cells were grown to confluence by incubation for anadditional 48 h as above. At 96 h after seeding, the medium was decantedand replaced with 1.3 L of infection medium (40% OptiPro in DPBS with0.5× cholesterol, 50 mM sucrose) and vaccine inoculum at a multiplicityof infection (MOI) of 0.01. Infection was allowed to proceed at 34° C.for 72 h (+/−4 h). Both MOI and time of harvest were optimized to ensuremaximal production of HSV529.

Example 2. Ultracentrifugation-Based Purification Scheme

Prior to the development of the purification disclosed herein, theconventional method for purifying HSV involved ultracentrifugation. Inthe case where mechanical cell disruption was used to liberate HSV529from the biomass, infected cells were detached from the substrate bymanual disruption of the monolayer at 72 hours post infection (hpi).Cells were poured from the NCF and a cell pellet was prepared bycentrifugation at 1,000×g. It was determined that at this point in theprocedure it is possible to freeze the HSV529-containing cell pellet at−80° C. without an appreciable loss in titer, for storage prior toprocessing. The cell pellet from a single NCF was brought to 1 L withstabilization buffer (50 mM potassium glutamate, 10 mM L-Histidine, 160mM NaCl, 10% sucrose, pH 7.0). The cell suspension was processed using amicrofluidizer (Microfluidics Corporation, Newton, Mass.) at 3,000 psi,on ice to mechanically disrupt cells and shear cellular genomic DNA. Thesolution was adjusted to 5 mM MgCl₂ and 15,000 units of Benzonase®endonuclease (EMD/Merck, Darmstadt, Germany) were added to theHSV529-containing solution. The Benzonase® reaction was allowed toproceed at 25° C. for 4 h. The cellular lysate was then clarified bycentrifugation at 5,000×g for 30 min at 4° C. Subsequently, the clearedcellular lysate was concentrated by flat sheet TFF on a Pellicon® XL50microfiltration system (Millipore, Bedford, Mass.). Three Pellicon® XL50cassettes (Biomax, 30 kDa, Polyethersulfone, 50 cm²) were mounted on aLabscale™ TFF System (Millipore) using the multi-manifold accessory. Thevolume of the solution was reduced from ˜1100 mL to ˜50 mL. Throughoutfiltration, the inlet pressure was maintained at 30 psi, while backpressure was increased from 1 to 8 psi as needed to achieve a practicalflux. Finally, the TFF retentate was subjected to ultracentrifugationfor 4 h at 50,000×g and 4° C. over a 25% sucrose cushion, prepared inDPBS with CaCl₂ and MgCl₂. The HSV529-containing pellet was finallyresuspended in stabilization buffer with 20% sucrose prior to beingaliquoted, flash frozen on dry ice/ethanol and stored at −80° C. HSV529prepared by this conventional, centrifugation-based method results incrude material with greater than 2 μg of residual host cell DNA per1×10⁷ PFU of HSV529.

Example 3. Dextran Sulfate

When mechanical cell disruption (sonication) was used prior tochromatographic separation the resultant virus was high in dsDNA, 0.33or 2.0 μg/mL by dsDNA assay, for samples which either were or were nottreated with Benzonase®, respectively) and the recovery of the virus waspoor (12% recovery for Benzonase®-treated samples and 39% for thosewhich had not been treated with Benzonase®) (see Table 2 below). Basedon these results, a non-mechanical means to harvest the virus from theproduction cells was tested. Ultimately, dextran sulfate was selected asthe best option for harvesting virus from the production cells. Testingwith dextran sulfate was first conducted in small-scale, 12-well plates,followed by a scale up to NUNC Cell Factories (NFC).

12-Well Plates

In the small-scale testing, when cells exhibited ˜100% cytopathic effect(CPE), as characterized by rounding of the cells, but remained attached(72 hpi) HSV529 was harvested by treatment with dextran sulfate. Initialdevelopment of the HSV529 viral harvest (dextran sulfate (DS) elution)procedure was performed in 12-well tissue culture plates. Parameterswhich were tested and/or optimized include: buffer (conditioned culturemedia, citrate and glutamate+histidine), pH (6.5-7.5), DS concentration(0-500 μg/mL), dextran sulfate molecular weight (5-5,000 kDa), degree ofsulfation (dextran sulfate vs. heparin), temperature (34 and 37° C.),osmolality (0-30% sucrose), agitation (+/−), time (3, 5, 8 and 24 h) andtiming (2-3 days post infection (dpi)) of release.

For screening purposes, infection medium was decanted from AV529-19cells in 12-well plates at either day 2 or day 3 after infection. Themedium was replaced with 600 pt of dextran sulfate elution buffer:stabilization buffer at pH 7.5 containing 0, 25, 50, 100, 200 or 500μg/mL dextran sulfate (MW ˜5 kDa) (Polydex Pharmaceuticals, Toronto,Canada). The plates were incubated at 34° C. for 3, 5, 8 or 24 h beforeharvest. Dextran sulfate-released HSV529 was prepared for potencytesting by centrifugation at 1,000×g to remove cells and cellulardebris.

FIG. 2 shows the result of a single representative screening experimentto address whether HSV529 could be eluted from the surface of AV529-19cells using dextran sulfate (DS). Indeed, when cells at 3 dpi wereincubated with DS, one could detect infectious material in thesupernatant after 24 h of incubation when ≥25 μg/mL of DS was used (FIG.2B). A concentration of 100 μg/mL DS was selected for further studies.

NUNC Cell Factories

In the larger-scale testing, at 72 hours post infection (hpi), theinfection media was decanted from a NCF into a container (2 L PETGBottle) for disinfection and disposal, and a small aliquot was retainedfor potency testing. A sterile, disposable funnel was placed into theNCF inlet port, and 600 mL of pre-warmed (34° C.) Dextran SulfateElution Buffer (50 mM potassium glutamate, 10 mM histidine, 0.16 Msodium chloride, 100 μg/mL dextran sulfate MW 6-8 kDa, 10% sucrose, pH7.5) was poured into the NCF. The NCF was placed on its side briefly, inorder for the elution buffer to evenly distribute between the layers.The NCF was flipped into the upright position and placed into ahumidified, 5% CO₂ incubator at 34° C. for 24 h. After 24 h ofincubation, the elution buffer was decanted from the NCF into a 1 L PETGbottle. The liquid was then evenly distributed into 250 mLconical-bottomed centrifuge tubes and centrifugation was performed for20 min. at 1,000×g in a centrifuge equipped with a swinging bucketrotor. The supernatant was decanted and placed into a fresh 1 L PETGbottle for subsequent Benzonase® endonuclease digestion. At this pointin the procedure it is possible to quick freeze (on liquid nitrogen) thematerial for storage at −80° C. until future processing. Freezing wasperformed without agitation.

The optimized procedure for large (NCF) scale release of HSV529 fromAV529-19 cells was as follows: at 3 dpi the infection medium wasdecanted; a sterile, disposable sterile funnel was placed into the NCFinlet port, and 600 mL of pre-warmed (34° C.) dextran sulfate elutionbuffer (stabilization buffer at pH 7.5 containing 100 μg/mL of DS with aMW of ˜5 kDa) was poured into the NCF. The NCF was incubated 24 h in ahumidified, 5% CO₂ incubator at 34° C. without agitation. After 24 h ofincubation, the elution buffer was decanted from the NCF and clarifiedby centrifugation for 20 min at 1,000×g. It was determined that at thispoint in the procedure it is possible to freeze HSV529-containingharvest fluid at −80° C. without a loss in titer.

Example 4. Endonuclease Digestion

If previously frozen, dextran sulfate (DS)-released material from oneNCF was removed from the −80° C. freezer and quick-thawed by placing ina 37° C. water bath. Gentle agitation by inversion was performed at ˜10min intervals to ensure that the sample did not overheat while melting.The volume of the material was measured and the solution was adjusted to5 mM MgCl₂ using a 1 M MgCl₂ stock solution. Ninety units of Benzonase®were added per mL of HSV529-containing solution. The solution was gentlymixed by inversion and placed in the incubator at 25° C., 80 rpm for 4-6h.

Benzonase® endonuclease treatment of HSV529 substantially increases thepurity of infectious virus after chromatography by Mustang® Q, asobserved by agarose gel electrophoresis of purified virus with orwithout Benzonase® treatment (data not shown). The desirability of aBenzonase® endonuclease digestion step was confirmed at the small scale(about 20 mL). Nine (9) T225 flasks of infected AV529-19 cells werereleased by incubation with 100 μg/mL dextran sulfate (1926: 04).Released material was clarified by centrifugation at 2,000×g and the 193mL supernatant was split into 2×96.5 mL aliquots. 1×96.5 mL wasimmediately filtered using 25 mm syringe filter units with low proteinbinding Supor membrane (a total of seven filters were used due tofrequent fouling of the membrane). The 87.5 mL untreated sample was thenapplied to a 0.35 mL small scale Mustang® Q chromatographic membrane(coin) and eluted with a 160 mM-2M NaCl gradient in stability buffer,with manual hold steps to allow for elution of protein-containingmaterial. The other aliquot was brought to 5 mM MgCl₂ and 90 U/mLBenzonase®. The solution was incubated for 4 h at room temperature(uncontrolled, on bench), and then held overnight at 4° C. Just prior toMustang® Q chromatography the Benzonase-treated sample was filtered asabove, 93.5 mL of sample was applied to the Mustang® Q coin and elutionwas performed as described previously (1926: 5-7). Individual elutionfractions were analyzed by agarose gel electrophoresis (1.5%), SDS-PAGE(4-20% Tris-Glycine) and plaque assay.

At the small scale, dead end filtration of material which had not beentreated by Benzonase® resulted in a ˜50% recovery of infectious titer,whereas filtration of material post-Benzonase® treatment resulted in amuch better (˜100%) step yield. In contrast, more of thenon-Benzonase®-treated material was recovered by Mustang® Qchromatography than Benzonase®-treated; ˜95% as compared to ˜75%, asshown in Table 2 below. Overall yield for each process was similar, butlosses were sustained at different points along the downstreampurification train. Based upon these observations, clarification of thebulk dextran sulfate-released material by depth or dead-end filtrationshould be performed after endonuclease treatment to prevent fouling ofthe filter and loss of titer. Additionally, Benzonase® treatment shouldbe performed to ensure that final purified material is low incontaminating DNA.

Example 5. Depth Filtration

Prior to performing chromatography, the Benzonase®-treated solution isfurther clarified to remove any remaining intact cells or cellulardebris or other aggregated material that might clog the chromatographicmembrane. The depth filtration manifold was assembled as schematizedbelow, using ¼″ sterile flange fittings (tri-clover to hose-tail barb)(with the requisite gaskets and tri-clover clamps) as well as size 24silicone MasterFlex tubing. The entire manifold, excluding pump, wasautoclaved for 25 min. at 121° C. dry, as recommended by themanufacturer. The Benzonase®-treated sample was passed though theautoclaved depth filter at 50 mL/min, without pretreatment orpreequilibration of the membrane. The membrane was vented until liquidwas observed coming out of the vent. Depth-filtered material wascollected in a sterile 1 L PETG bottle, and was stored at 4° C.overnight before chromatographic separation from contaminants.

Example 6. Anion Exchange Chromatography

At the NCF scale, the chromatography flowpath was assembled with size 25silicone MasterFlex (Cole Parmer) tubing and 1½″ sterile flange fittings(tri-clover to host-tail barb) with associated gaskets and tri-cloverclamps. The flowpath, including the chromatographic membrane wasprepared and chemically sterilized as per the manufacturers'instructions. Briefly, the membrane (10 mL Mustang® Q capsule, PallCorporation, Port Washington, N.Y.) was wet with filter-sterilizedreverse osmosis deionized (RODI) water while venting. Subsequently, themembrane was sterilized and preconditioned at 100-200 mL/min with 500 mL0.5 M NaOH and 500 mL 1 M NaCl, respectively. Chromatography runningbuffer was comprised of stabilization buffer at pH 7.0 with theconcentration of sodium chloride described for each step. The membranewas equilibrated with low salt (0.16 M NaCl) column equilibrationbuffer, until the pH and conductivity of the outlet stream matched thatof the original buffer (˜1.5 L of buffer). All subsequent chromatographysteps were performed at 60 mL/min. Initially, the HSV529-containingsample was loaded onto the membrane, and a flowthrough fraction wascollected, the membrane was then washed with equilibration buffer untilthe UV (280 nm) trace returned to baseline and a two-step salt elutionwas performed. Pre-elution of impurities was performed with 0.7 MNaCl-containing buffer. The pure, infectious, HSV529-containing fractionwas eluted from the membrane with 2 M NaCl-containing buffer.Originally, infectious virus was eluted from the membrane in two steps(1.4 and 2 M NaCl). Subsequent analysis revealed that the two steps hadcomparable purity, and the higher salt concentration (2 M NaCl) waschosen to elute HSV529 in a single higher titer step. All fractions werecollected manually while observing the absorbance at 280 nm on a chartrecorder. An in-line digital pressure monitor was used to ensure thatthe pressure remained below 94 psig (maximum operating pressure).

Determination of the optimal chromatographic support for bind-and-elutechromatography was performed in a series of small-scale screeningexperiments, with the primary intention of attaining maximum yield ofinfectious virus in the eluted fraction. Table 2 below shows anon-exhaustive list of yields from such screening experiments.

TABLE 2 Virus step yield (PFU) from small-scale screening of anionexchange purification conditions (harvest method, chromatography resins,etc.) Harvest Resin Benzonase ® Step Yield Microfluidization CIM ® DEAE−  5% CIM ® Q −  2% Sonication Capto ™ Q − 31% Capto ™ Q + 12% HiTrap ™DEAE FF − 10% Mustang ® Q − 39% Mustang ® Q + 12% Dextran SulfateMustang ® Q − 95% Mustang ® Q + 75% Fractoge ®l DEAE + 61% Fractogel ®TMAE + 59% Fractogel ® TMAE HiCap + 67% CIM ® DEAE + 15% CIM ® Q +  6%CIM ® EDA +  6% UNOsphere ™ Q + 22% Capto ™ Q + 65% GigaCap ® Q + 44%

Overall yield (presented as the number of human doses (1×10⁷ PFU) perNCF) for HSV529 purifications from optimization experiments (labeledPreparations A-G) are presented as FIG. 4. The overall yield increasedas chromatography and other purification conditions were optimized.Replacement of the Mustang® Q membrane-based anion exchanger with abead-based tentacle resin (Fractogel TMAE HiCap, EMD Merck) resulted ina non-significant increase in yield and lower purity (compare HSV529Preparations F and G in FIG. 5B-D).

Additional modifications tested in the small scale studies presentedhere include the use of dead end filtration (0.8 μm, 25 mm, supormembrane, syringe filter (Pall Corporation)) as a substitute for depthfiltration and dialysis in slide-a-Lyzer® cassettes (Thermo-FisherScientific (Pierce Protein Research Products), Rockford, Ill.) MWCO10-20 kDa for buffer exchange instead of TFF.

While a wide variety of alternative approaches were attempted,ultimately dextran sulfate release, Mustang® Q and hollow fiber TFF wereused for purification. Examples of chromatography chemistries and resinswhich were considered inadequate for reasons of yield or purity afterassessment at small (20-50 mL) scale are as follows: HiTrap™ Heparin HP(GE Healthcare), Cellufine® Sulfate (CHISSO Corporation, Tokyo, Japan),HiTrap™ Capto™ Q (GE Healthcare), GigaCap® Q (TOSOH, Yamaguchi, Japan),UNOsphere™ Q (Bio-Rad, Hercules, Calif.), Fractogel® [DEAE, TMAE andTMAE HiCap] (EMD/Merck), CIM® [Q, DEAE, EDA, and SO₃] (BIASeparations,Villach, Austria), etc.

Since the maximum yield was obtained with the Mustang® Q membrane, thiswas chosen for scale up to purification of material from a single NCF.FIG. 3 shows the chromatographic profile for elution of HSV529(DS-harvested, Benzonase®-treated, and dead-end filtered) prior toloading onto the Mustang® Q coin (0.35 mL) on an ÄKTA Explorer (GEHealthcare, Piscataway, N.J.). The flow rate was 3 mL/min and stepelution was performed automatically over 30 column volumes (CV). TheHSV529 containing fraction is eluted from the support at 100% B or 2 MNaCl, as labeled.

Example 7. Concentration and Filtration

As noted above, FIG. 4 shows the results of a series of small-scaleoptimization experiments in which various purification parameters werealtered to observe the effect on HSV529 yield. Major changes whichpositively impacted the yield are highlighted by boxes and include theswitch from a flat sheet TFF system to a hollow fiber TFF system. Yieldwas effectively doubled by switching from flat sheet TFF with thePellicon XL system to hollow fiber TFF with the Kros-Flo system (FIG. 4,horizontal boxes). It is thought that the increase in yield is due to alower shear force being generated by open-channel flow as opposed to theflat sheet system where a turbulence generating screen in the flow pathacts to maximize flux by minimizing formation of a gel layer. The hollowfiber TFF module which was used in the experiments presented here had aMWCO of 100 kDa, we also tested a 500 kDa MWCO cassette but yield wasconsistently lower than what is described here (data not shown).

At the NCF scale, the 2 M NaCl elution fraction was concentrated(5-10-fold by volume) and buffer-exchanged into the final formulation bydiafiltration against 3-5× the volume of stabilization buffer containing20% sucrose. This was performed by hollow fiber tangential flowfiltration (100 kDa MWCO, 85 cm², polysulfone hollow fiber TFF module,Spectrum Laboratories, Rancho Dominguez, Calif.) on a Kros-Flo® ResearchII system, although in initial optimization experiments (labeledpreparations A-D for the purposes of this report) flat sheet TFF wasperformed as described above. In order to minimize shear, the lowestsuggested flow rate was utilized (130 mL/min, which equates to a shearrate of 4,000 s⁻¹). The transmembrane pressure (TMP) was kept below 4psi throughout the diafiltration process to minimize formation of a gellayer, which could impede fluid flux. As before, the finalHSV529-containing material was aliquoted, flash frozen on dryice/ethanol and stored at −80° C. Due to the large size of the HSV-2virus particle (180-200 nm), sterile filtration of the final material isnot possible. For this reason, all manipulations should be performedunder aseptic conditions.

Example 8. Titration of HSV529

Infectivity of HSV529 was assessed by titration of samples on thecomplementing cell line. 12-well tissue culture plates were seeded oneday prior to inoculation with 4×10⁵ cells per well. Samples wereserially diluted, plated and incubated 1 h, 37° C., 5% CO₂, with gentlerocking every 15 min. One mL of methyl cellulose overlay medium (in DMEMsupplemented with L-glutamine, heat-inactivated FBS and antibiotics) wasadded to each well and the plates were incubated 48 h. Plaques werevisualized by staining with 1% crystal violet in 70% methanol. Aftermanual counting of plaques, titers were represented as plaque formingunits (PFU)/mL.

Example 9. HSV529 Purity Assays (ELISA, qPCR, and PicoGreen dsDNA)

Commercially available ELISA was utilized to determine the purity ofprocess retains as well as of purified HSV529. ELISAs against Benzonase®(EMD/Merck), Vero Host Cell Protein (HCP) (Cygnus Technologies,Southport, N.C.) and dextran sulfate (Lifespan Technologies, Salt LakeCity, Utah) were used. Assays were performed as per the manufacturer'sinstructions, except that the following diluents were used in the samplepreparation in cases where the diluent was not specified: Vero HCP ELISA(50 mM Tris, 0.1 M NaCl, 8 mg/mL bovine serum albumin, pH 7.0) and DSELISA (1× phosphate buffered saline (PBS), pH 7.4). Assay specificlimits of detection (LOD) are 0.1 ng/mL (Benzonase®), 2 ng/mL (Vero HCP)and 0.003 μg/mL (DS).

Residual Vero DNA testing of HSV529 samples was contracted to WuXIAppTec, Inc. (Philadelphia, Pa.) on a sample-by-sample basis. Briefly,the assay is a quantitative PCR (qPCR)-based GLP/GMP assay using ABIFast 7500 Taqman® technology. Results were provided in the form of afinal report, indicating the amount of residual Vero DNA for threenested ribosomal RNA amplicons of 102, 401 and 765 base pairs (bp). Forthe purposes of this study, the assay was performed at the researchlevel (non-GMP). Data representing the 102 bp amplicon are presented inthe results section of this report. The limit of quantitation (LOQ) forthis assay is ≤1 pg/μL. Some samples were assayed for dsDNA contentusing the Quant-iT™ PicoGreen dsDNA Assay Kit (Invitrogen) as per themanufacturers instructions.

Mustang® Q-purified material (HSV529 Preparation F) contained less Veroresidual DNA (FIG. 5B), dextran sulfate (FIG. 5C) and Vero HCP (FIG. 5D)than the Fractogel TMAE HiCap purified material (HSV529 Preparation G).To look more specifically at the benefits to using each step in thepurification train, Tables 3 and 4 below highlight the yield and purityresults for each step of the HSV529 Preparation A purification.

TABLE 3 Vero DNA HCP DS Yield (ng/ (μg/ Benzonase ® (μg/ Retain (%)dose) mL) (ng/mL) mL) Start 45 ^(a) 75 <LOD 28 Benzonase ® 85 ^(a) 12752 27 Depth Filter 108 nd 104 51 11.25 Mustang ® Q FT 0 nd 91 47 <LODMustang ® Q Wash 0 nd 7 4 <LOD Mustang ® Q Step 1 0.1 nd 9 <LOD <LODMustang ® Q Step 2 31 <10 6 <LOD <LOD Mustang ® Q Step 3 29 <10 3 <LOD<LOD TFF Permeate 0 nd 0 <LOD <LOD TFF Retentate 38 9.74 30 <LOD <LOD^(a) We were unable to determine the amount of Vero DNA in the startingmaterial, as even at high dilutions there was 100% interference of qPCRsignal by the sample (dextran sulfate and/or Benzonase ®).

TABLE 4 Vero HCP Purification Retain (μg/mL) (total mg) (PFU/mg) FactorStart 75 75 1.5 × 10⁵  1x Benzonase ® 127 75 1.2 × 10⁵  1x Depth Filter104 60 1.7 × 10⁵  1x Mustang ® Q FT 91 53 0 — Mustang ® Q Wash 7 3 0 —Mustang ® Q Step 1 9 1 3.4 × 10⁴ — Mustang ® Q Step 2 6 1 9.2 × 10⁶  60xMustang ® Q Step 3 3 0.3 3.1 × 10⁷ 200x TFF Permeate <LOD — — — TFFRetentate 30 0.5 3.7 × 10⁷ 250x

As previously mentioned, improvements to the yield (FIG. 4) were made byswitching from flat sheet to hollow fiber TFF. Depth filtration appearsto partially remove dextran sulfate from the feed stream, the rest ofwhich is removed during chromatography (Table 3, column 6). Also, as wasexpected, Benzonase® was removed during chromatography as it does notbind to anion exchangers at neutral pH (Table 3, column 5). Although wewere unable to determine the amount of Vero DNA in the starting materialdue to 100% interference of the qPCR signal by the sample (as measuredby an internal E. coli DNA spike control), we were able to show thatafter Benzonase® treatment, depth filtration and chromatography, theamount of Vero DNA in the sample was less than the WHO limit per humandose of vaccine (Table 3, column 3). Finally, the majority of Vero HCPwas removed during chromatography (flowthrough, wash and pre-elution;Table 3, column 4). Inspection of the purification factor (PFU per mg ofVero HCP) for HSV529-containing fractions shows a 250-fold purificationof HSV529 with respect to Vero HCP (Table 4).

Example 10. Chromatography-Purified HSV529 is as Immunogenic andProtective as Sucrose Cushion-Purified HSV529 In Vivo

All procedures were performed according to IACUC-approved protocols.Subcutaneous (sc) immunization of female BALB/c mice (Charles River,Wilmington, Mass.) 6-7 weeks old was performed in the scruff of the neckon days 0 and 21 of the study. On day 0, animals were injected with 100μL sterile PBS (group 3) or with 1×10⁶ PFU of HSV529, either sucrosecushion-purified (group 1) or chromatography-purified (group 2), dilutedto 100 μL with sterile PBS. On day 34 of the study, mice were injectedsc with 2 mg depot medroxyprogesterone acetate (Depo-Provera, DMPA)(SICOR Pharmaceuticals Inc., Irvine, Calif.) in PBS. Seven days later,mice were challenged intravaginally with 50 LD₅₀ (8×10⁴ PFU) of HSV-2strain 333 in 20 μL with a positive displacement pipet. HSV-2 strain 333was a generous gift from Dr. Jeffrey Cohen (NIAID, Medical VirologySection). Animals were observed for 14 days post challenge. Mice wereeuthanized upon observation of purulent genital lesions. Animals werebled on days 18, 35 and 41 of the study.

Endpoint ELISA titers against HSV-2 purified viral lysate (AdvancedBiotechnologies, Colombia, Md.) were determined for serum from day 35samples. Plates (96 well Maxisorp, Nalge NUNC International, Rochester,N.Y.) were coated with 100 μl/well of HSV-2 viral lysate at aconcentration of 2 μg/mL. Serum IgG was detected with 1:2,000biotin-anti-mouse IgG Fc (Sigma-Aldrich, Saint Louis, Mo.) diluted in 1%BSA, 0.05% Tween in PBS. Time resolved fluorescence (TRF) signal wasmeasured using a Victor II fluorometer (Perkin Elmer, Waltham, Mass.)after addition of 0.1 μg/mL Dissociation-Enhanced Lanthanide FluorescentImmunoassay (DELFIA) europium-streptavidin conjugate in DELFIA AssayBuffer.

Female BALB-c mice were immunized subcutaneously with two doses ofHSV529 prepared either by sucrose cushion ultracentrifugation or bychromatography (Preparation F). A lethal challenge study was carried outas schematized in FIG. 6A. Serum from blood taken one week after thesecond and final vaccine dose was tested for IgG response against acommercially available viral lysate. After two immunizations, bothpreparations elicit a similar anti-HSV-2 IgG response (FIG. 6B; P=0.99,one way ANOVA, Kruskal-Wallis test). Two weeks after the lastimmunization, animals were treated with medroxyprogesterone and, sevendays later, given a 50×LD50 intravaginal challenge with wild type HSV-2strain 333 (FIG. 6C). The sucrose cushion ultracentrifugation-purifiedvaccine and the chromatography-purified vaccine afforded statisticallyequivalent protection of 80% and 70%, respectively, while mockimmunization resulted in complete lethality (0% survival; P<0.0001). Asubsequent study with chromatography-purified HSV529 revealed thatcomplete protection from challenge was achieved when immunization wasperformed intramuscularly.

It must also be noted that, as used in this disclosure and the appendedclaims, the singular forms “a”, “an”, and “the” include plural referentsunless the context clearly dictates otherwise. Optional or optionallymeans that the subsequently described event or circumstance can orcannot occur, and that the description includes instances where theevent or circumstance occurs and instances where it does not. Forexample, the phrase optionally the composition can comprise acombination means that the composition may comprise a combination ofdifferent molecules or may not include a combination such that thedescription includes both the combination and the absence of thecombination (i.e., individual members of the combination). Ranges may beexpressed herein as from about one particular value, and/or to aboutanother particular value. When such a range is expressed, another aspectincludes from the one particular value and/or to the other particularvalue. Similarly, when values are expressed as approximations, by use ofthe antecedent about, it will be understood that the particular valueforms another aspect. It will be further understood that the endpointsof each of the ranges are significant both in relation to the otherendpoint, and independently of the other endpoint. All references citedin this disclosure are hereby incorporated herein in their entirety.

What is claimed is:
 1. A composition comprising Herpes Simplex Virus(HSV) particles in a liquid stabilization buffer, wherein the liquidstabilization buffer comprises glutamate, 1-20 mM histidine andoptionally glutamine, a salt, and a sugar, and wherein other thanhistidine and optionally glutamine, the liquid stabilization buffer doesnot contain any other amino acids.
 2. The composition of claim 1,wherein the liquid stabilization buffer comprises 20-75 mM potassiumglutamate, 1-20 mM histidine, 50-250 mM salt, and 5-20% sugar.
 3. Thecomposition of claim 2 wherein the liquid stabilization buffer comprises50 mM potassium glutamate, 10 mM histidine, 160 mM salt, and 10% sugar.4. The composition of claim 3, wherein the sugar is sucrose.
 5. Thecomposition of claim 2, wherein the pH of the liquid stabilizationbuffer is about 7.5.
 6. The composition of claim 2, wherein the HSV is areplication defective HSV.
 7. The composition of claim 6, wherein thereplication defective HSV is HSV529.
 8. The composition of claim 2,wherein the residual host cell DNA in said composition is less than 10ng host cell DNA per 1×10⁷ PFU.
 9. The composition of claim 2, whereinthe composition contains greater than 1×10⁷ PFU/mL.
 10. The compositionof claim 2, wherein the composition contains between about 1×10⁷ to2×10⁷ PFU/mL.
 11. The composition of claim 2, wherein the sugar issucrose.
 12. The composition of claim 3, wherein the pH of the liquidstabilization buffer is about 7.5.
 13. The composition of claim 12,wherein the residual host cell DNA in said composition is less than 10ng host cell DNA per 1×10⁷ PFU.
 14. The composition of claim 13, whereinthe composition contains greater than 1×10⁷ PFU/mL.
 15. The compositionof claim 8, wherein the composition is a pharmaceutical compositionfurther comprising a pharmaceutically acceptable carrier.
 16. Thecomposition of claim 13, wherein the composition is a pharmaceuticalcomposition further comprising a pharmaceutically acceptable carrier.17. The composition of claim 1, wherein the liquid stabilization buffercomprises potassium glutamate.
 18. The composition of claim 1, whereinthe HSV is herpes simplex virus type-2 (HSV-2) or herpes simplex virustype-1 (HSV-1).